The present invention relates to a differential limiter for a vehicle, which comprises a mechanism for limiting a differential operation between wheels, e.g., a lock mechanism in a center differential apparatus and, more particularly, to a differential limiter which aims at improvement of acceleration performance and engine brake performance by applying a differential limiting force in accordance with a change in torque caused by a shift operation.
As a vehicle comprising a mechanism for limiting a differential operation between wheels, e.g., a lock mechanism in a center differential apparatus, a technique disclosed in, e.g., Japanese Patent Laid-Open No. 62-244717 is known. In a vehicle according to this conventional technique, a transmission torque capacity of a differential limiter in a center differential apparatus is controlled in accordance with rotational speeds of wheels, and a shift position, thus assuring a driving force, and preventing a braking phenomenon at a tight corner.
On the other hand, Japanese Patent Laid-Open No. 62-261536 discloses another technique. In this technique, when a shift range is a range for generating an engine brake, a transmission torque capacity of a differential limiter of a center differential apparatus is increased as compared to other forward travel ranges, thus improving engine brake performance.
A common feature of the techniques disclosed in the above-mentioned references is that a differential limiting force is increased as a shift position is at a low position (high gear ratio). The differential limiting force is increased depending on a shift position. However, a shift operation, e.g., a shift-down operation, is performed to obtain predetermined engine brake performance and acceleration performance, and a change in torque in a transient period during the shift operation poses a problem. In other words, as disclosed in the above-mentioned references, even if a differential limiting force is controlled in consideration of only a shift position after a shift operation, a proper limiting force cannot be obtained. Therefore, desired acceleration performance and engine brake performance cannot be obtained, and a demand for improvement in this respect has arisen.